Online Brokers OptionsHouse, tradeMonster Merge

Private-equity specialist General Atlantic, which provided early financing to E*Trade, will bring OptionsHouse and tradeMonster together.

Two of our favorite online brokers for options traders, OptionsHouse and tradeMonster, are merging in a deal engineered by private-equity firm General Atlantic, which has a substantial financial-services portfolio and previously owned stakes in the New York Mercantile Exchange, the New York Stock Exchange, and online broker E*Trade.

PEAK6, OptionsHouse's parent, will sell the broker to General Atlantic, which will simultaneously acquire a majority stake in tradeMonster. The merger, expected to be finalized in the third...